This invention generally relates to instruments used by the downhole industry to determine pressure and temperature. More specifically, the invention relates to quartz-based instruments used by the downhole industry to determine pressure and temperature.
Existing quartz-based instruments used by the downhole industry utilize systems with multiple quartz resonating elements to determine pressure and temperature. Typically, such systems consist of one pressure sensor (responsive to both pressure and temperature), one reference sensor (exposed to temperature and isolated from pressure) and one temperature sensor (exposed to temperature and isolated from pressure). The reference sensor is less sensitive to temperature as compared to the temperature sensor.
Using mixer oscillators (see e.g., U.S. Pat. No. 5,166,645) the signals from the sensors are processed and the resulting data is either stored on a memory chip on board the gauge or is sent uphole through a power cable or a tubing encapsulated conductor (“TEC”) cable to the surface equipment (see FIG. 1). There are a large number of electronic components which have to survive high temperatures downhole, making the gauge expensive as well as prone to failures in the field.